Support systems for stator end windings of turbine generators must absorb vibration. The support system must control the forces which result from both steady-state and short-circuit conditions, and also allow controlled axial motion for thermal expansion. Atkinson et al., in U.S. Pat. No. 2,427,700, taught resin impregnated spacer blocks between adjacent end windings, to prevent end winding movement relative to one another during generator operation. The spacer blocks were made from a fibrous material, such as asbestos cloth, impregnated with a carbon filled phenolic resin.
Since the time of Atkinson et al., sophisticated bracing systems involving, in part, hoses filled with latent catalyzed epoxy resins, have been used between end turn layers. Prior to filling these hoses, the spaces between adjacent end turns within each end turn layer must be partially braced with resin impregnated stator end winding spacers. The use of resin filled hose bracing systems presents unique problems in formulating a suitable composition for impregnating the stator end winding spacers. The resin system must display a moderately low initial viscosity, have at least a 3-hour shelf life, meet toxicity standards, exhibit behavior of a non-running material of essentially solid form within one day of compounding, remain compliant for about 3 weeks, not drip on subsequent heating under pressure while displaying adequate flow so as to conform and bond to the windings, and cure at about 125.degree. C. to give a heat distortion temperature of at least about 200.degree. C.
No true B-stage system, such as an epoxy resin system, meets all of these requirements. What is needed is a resin system specially formulated to meet the unique demands required of stator end winding spacer impregnants in sophisticated resin filled hose bracing systems used in turbine generators.